1. Field of the Invention
This invention relates to a free-standing, porous foam product comprising an integral network of polyvinylpyrrolidone (PVP) molecules hydrogen-bonded to hydrogen peroxide (H.sub.2 O.sub.2) molecules, and to a method of making such products.
2. Description of the Prior Art
Stabilized H.sub.2 O.sub.2 compositions have found wide utility in commercial and industrial applications, e.g. as antiseptics, disinfectants, sterilization agents, bleaching materials, washing concentrates, etchants, in cosmetic preparations, as cigarette filters, and as a catalyst in polymerizations requiring a free radical source. In biological applications which require an antiseptic, disinfectant or sterilization agent, such H.sub.2 O.sub.2 compositions require release of an effective amount of oxygen at a desired rate.
Shiraeff, in U.S. Pat. Nos. 3,376,110 and 3,480,557, prepared various compositions of PVP and H.sub.2 O.sub.2 by mixing an aqueous solution of PVP and a substantial excess of H.sub.2 O.sub.2, and evaporating the solution to dryness at 90-100.degree. C. The H.sub.2 O.sub.2 content of the compositions obtained, however, was quite variable, ranging from 2% to 70% by weight, and considerable water was present in the final composition. Prolonged drying of the composition, in an attempt to reduce its water content, resulted in a further loss of H.sub.2 O.sub.2. The resultant product was described as a brittle-film, or a transparent, gummy, amorphous material.
Merianos, in U.S. Pat. No. 5,008,093, provided free-flowing, stable, high purity, substantially anhydrous powders of PVP and H.sub.2 O.sub.2 in defined molar ratios of 1:1 or 2:1. These free-flowing products were made by reacting a suspension of PVP and a solution of H.sub.2 O.sub.2 in an anhydrous organic solvent, such as ethyl acetate. The free-flowing PVP-H.sub.2 O.sub.2 powders made by Merianos represented a significant advance in this art because the peroxide content was reproducible.
Biss, in U.S. Pat. No. 5,077,047, described a commercial process for the production of such free-flowing powders wherein a fluidized bed of PVP powders was maintained at a reaction temperature of from ambient to 60.degree. C. and contacted with finely-divided droplets of an aqueous H.sub.2 O.sub.2 solution containing about 30 to 85% by weight hydrogen peroxide. The resultant product was a stable, substantially anhydrous, free-flowing powder of 1:1 molar ratio PVP-H.sub.2 O.sub.2.
Rainer, in U.S. Pat. No. 4,182,743, described a filter material for selective removal of aldehydes from cigarette smoke which consisted of a gas-permeable substrate or carrier, such as silica gel, on which a film of a composition of concentrated H.sub.2 O.sub.2, PVP and water was formed. The film was made by applying an aqueous solution of H.sub.2 O.sub.2 and PVP onto the carrier material, and drying in a vacuum oven or desiccator at room temperature.
These and other methods described in the art, however, have not provided a free-standing, porous foam product of PVP and H.sub.2 O.sub.2, optionally including a water-soluble gelling agent, by freeze-drying an aqueous solution of H.sub.2 O.sub.2 and PVP, optionally with the gelling agent, and removing the water under predetermined process conditions which enable the formation of such a free-standing, porous foam product.